Case of Pseudohypoglycemia

The patient is a 44-year-old white woman with a history of myasthenia gravis, hypothyroidism, epilepsy, and Raynaud’s phenomenon.
In May 2000, while hospitalized for gastroenteritis, a fingerstick glucose reading reported as “low.” Subsequent outpatient
testing showed a normal random venous glucose level with concurrent normal C-peptide and insulin levels. The patient obtained
a One Touch glucose meter and continued to monitor her glucose frequently for the next few months. The glucose readings were
consistently 30–40 mg/dl. She often reported symptoms of lightheadedness, fatigue, and sweating, but in retrospect, the relationship
between these symptoms and the glucose readings was inconsistent.

A second endocrinologist repeated the glucose and C-peptide tests, and these were again normal. A urine screen for sulfonylurea
agents was negative.

The patient was then referred for a prolonged fast. On greeting the patient, her hands were white and cold. Over the subsequent
2 h, using a Freestyle meter (FM) and a Precision QID meter (PM), glucose measurements were obtained from the patient’s fingertips
and forearms and by venipuncture.

At 9:00 a.m., glucose levels from the fingertips were 53 and 56 (FM) and 49 and 38 (PM) mg/dl, and the forearm level was 83 mg/dl (FM).
At 10:00 a.m., glucose levels from the fingertips were 50 (FM) and 48 (PM) mg/dl, and the forearm level was 73 (FM) mg/dl. At 11:00 a.m., glucose levels from the fingertips were 42 (FM) and 53 (PM) mg/dl, and the forearm level was 78 (FM) mg/dl. Also, at 11:00
a.m., a venous blood sample was drawn. This sample was used for a glucose check on each meter and was sent to the clinical laboratory
(LAB). The 11:00 a.m. glucose levels from the venous sample were 88 (FM), 93 (PM), and 86 (LAB) mg/dl.